Control circuit for electron tubes



'A. CROSSLEY CONTROL CIRCUIT FOR ELECTRON TUBES Dec. 25, 1928.

Filed April 30, '1925 20 current aracteristic of the tube.

Patented Dec. 25. 1928.

UNITED STATES PATENT OFFICE.

ALFRED CROSSLEY, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIRED RADIO, mo,

01 NEW YORK, N. Y., A. CORPORATION OF DELAWARE.

CONTROL CIRCUIT FOR ELECTRON TUBES.

Application filed April 30, 1925. Serial No. 26,968.

My invention relates broadly to radio vacuum tube transmitters and more particularly to piezo-electric crystal control circuits for vacuum tube transmitters.

5 An object of my invention is to provide control circuits which associate a piezo-electric crystal with a vacuum tube transmitter to improve and regulate the operation of the transmitter and obtain a constant frequency emission for such vacuum tube transmitters.

Another object of my invention is to provide circuits in a piezo-electric crystaloscillation system which increase the output from the system for a given input.

Another object of my invention is to improve the eiiiciency of a piezoelectric crystal associated with vacuum tube transmitters by controlling the voltage of the grid circuit to the ne ative side of the grid voltage-plate fully Further objects will appear more hereinafter.

My invention consists substantially in the construction, combination and arrangement of parts and circuit arrangements associated therewith or as will be more fully hereinafter set forth, as shown by the accompanying drawings and finally pointed out in the appended claims.

Reference is to be had to the accompanying drawings forming a part of the specification hereinafter following in which like reference characters indicate corresponding parts throughout the several views and in which:

Figure 1 is a schematic diagram of my invention showing the use of a battery as a source of grid control;

Figure 2 is a similar view employing a resistance associated with a battery as a source 4 of grid control; and

Figure 3 shows the embodiment of my mvention in a completetube transmitter.

It has been found during experimental work conducted with piezo electrical .crystals, that these crystals will produce alimited amount of oscillating power when used as a i freqllliency controlling or oscillating device in t e grid circuit of a vacuum tube transmitter. In view of the limited amount of power available from the crystal it can be readily seen that any means provided to make best use of this power will produce maximum output from any piezo-electrical crystal vacuum tube transmitter.

Inasmuch as the power dissipated in the grid circuit .is mainly represented by the losses in the grid-filamentcircuit, it becomes necessary to prevent the flow of current between the grid and the filament. To prevent this flow of current I have placed a negative C voltage on the grid of such a magnitude as to prevent the crystal oscillating voltage from passing beyond the zero voltage point and becominga positive voltage- If such a condition is obtained the crystal-grid circuit will be working under a nolo-ad condition and the maximum output will be obtained from the transmitter. In practice, however, it is permissible to permit the positive alteration of the crystal oscillation to exceed the negative C voltage by a small 6 amount, thus allowing a, small amount of current to flow between grid and filament,

that is to say, the crystal is operated under a very small load.

The above conditions can only be obtained by employing some source of negative C.

voltage and lmp-ressing this voltage on the grid of the vacuum tube through a choke coil. y the use of the negative C voltage it has been found that very little attention need be given to the crystal once it has beenplaced in operation. The reverse has always been noted when anykind of crystal was used in circuits employing grid leaks 'or floating.

grid controls.

Referring more particularly to the drawings; 1 is a piezo-electrical crystal which has associated with it conventional metal contact plates; 2 is a choke coil which preventsthe flow of oscillating current through a negative C battery source, but at the same time allows the negative O voltage to be placed on the grid 3 is a battery or generator which j is capa le of supplying a steady source of voltage. As will be noted the negative terminal of this voltage source is connected direct to the choke coil 2. dis a vacuum tube which has associated with it a filament heating battery 5, a plate choke 6, plate battery 7, bypass condenser 11 for by-passing hi h freuency oscillations around battery 3, con- "enser 9, and oscillating circuit 8, alL of which comprise the plate circuit.

Figure 2 is similar to Figure 1 with the exception of the substitution of a resistance 10 circuit with filament heating battery?) in lieu of the battery 3. This resistance when connected between the ne ative terminal of the plate battery and the lament, functions as a source of negative 0 voltage because, With this condition, the filament is positive With respect to the end of the resistance connected to the negative termifial of the plate battery. As the grid is connected through the choke 2 to the negative terminal of the plate battery it must therefore be negative with respect to the filament. The value of this negative C is proportional of course, to the size of the resistance and the current flowing through it.

My invention is the outcome of numerous experiments with piezo-electrical crystals where all methods of grid control were tried. During these experiments 'a grid leak resistance was employed in place of battery 3, but it was found unsuitable for use with all types of crystals. With some crystals it produced the re uired output but with other crystals no osci lations could be obtained. This condition may be attributed to the fact that grid current must flow before the grid leak will function and under such a load condition only ver good crystals will oscillate The oating grid method, namely, the elimination of the choke 2 and the battery 3, from circuit shown in Fig. 1, was also tried but was found unsatisfactory from an output standpoint.

In Fig. 3 I have shown the application of my crystal control circuit to an electron tube transmitter where the oscillating circuit 8 is coupled to the input of the amplifier 12. Choke coil 15 and battery 16 may be arranged to suitably bias the grid circuit of tube 12. The output circuit of the amplifier 12 in cludes choke 17, battery 18 and by-pass condenser 23 and primary coupling system 19. The coupling system 19 delivers its energy to secondary inductance 20 in the antenna and ground system 21 and 22. While I have illustrated but one stage of amplification it will be understood that several stages may be employed in conjunction with the crystal control circuit.

In the operation of my invention I have found that a considerable increase in the output power is obtainable from the crystal control circuit at an extremely constant frequency enabling a radio transmitter to be set or radiation 0 energy on an extremely constant si aling frequency.

.It wil be understood that ahigh resistance can be substituted in place. of the choke coil 2 in Figures 1 and2without sacrificing any of the advantages of my invention.

While I have described my invention in certain particular embodiments, I desire it to be understood that modifications may be made. and that no limitations upon the invention are intended other than are imposed by the scope of the appended claims.

Having thus described my invention" what I claim is:

1. In a piezo electric crystal oscillating circuit, a crystal, a pair of metal contact plates on each side thereof, said plates being connected respectively to the grid and filament terminals of a vacuum tube, a choke coil, one end of which is connected to the negative terminal of a source of potential and so arranged that the opposite terminal of choke coil is connected to the grid of the vacuum tube while the positive terminal of said source of potential is connected direct to the filament of said tube, and a plate oscillating system which comprises the plate of the vacuum tube, a choke coil, aradio frequency by-pass condenser, a high potential source and a resonant circuit consisting of an inductance, a capacity and a resistance.

2. An electron tube oscillator comprising an electron tube having grid, filament and plate electrodes, an output circuit connected across said plate and filament electrodes, means controlling the frequency of said oscillator comprising a piezo electric crystal, said piezo electric crystal being in circuit with said grid and filament electrodes, means connected in shunt with said piezo electric crystal for preventing the crystal oscillating-voltage from passing substantially beyond the zero gridvoltage point and becoming a positive voltage and a resonant circuit connected across said output circuit for sustaining oscillations delivered by said piezo electric crystal at a frequency corresponding to the natural frequency of said piezo electric crystal.

3. A piezo electric crystal control and oscillator circuit comprising an electron tube having grid, filament and plate electrodes, a grid circuit and an oscillatory circuit connected with the electrodes of said electron tube, a piezo electric crystal element, connections between said piezo electric crystal element and said circuits for sustaining high frequency oscillations corresponding to the characteristic frequency of said piezo electric crystal element, a circuit connected in shunt with said piezo electric crystal element and in said input circuit for maintaining the current flow between said grid and filament electrodes substantially negligible and preventing thecrystal oscillatory voltage from passing beyond the zero voltage point and becoming a positive voltage, a choke coil and source of potential connected between.

said filament and plate electrodes, and a resonant circuit connected across said choke coil and source of potential, whereby said piezo electric crystal element operates under conditions of no load for de ivering maximum output to said resonant circuit.

ALFRED oRossLEY.

DISCLAIMER 1,696,626.Aljred Grossly, Washington, D. 0. Common CIRcUI'nQFoR ELECTRON TUBES. Patent dated December 25, 1928. Disclaimer filed April 29., 1933, by the assignee, Wired Radio, Inc. Hereby enters a disclaimer to the subject matter of the following claim, to wit:

In a piezo electric crystal oscillating circuit, a crystal, a pair of metal contact plates on each side thereof, said plates being connected respectively to the grid and filament terminals of a vacuum tube, an impedance element, one end of which is connected to one terminal of a source of potential and so arranged that'the opposite terminal of the impedance element is connected to the grid of the vacuum tube While the other terminal of said source of potential is connected direct to the filament of said tube, and a plate oscillating system which comprises the plateof theyacuum tube, a choke coil, a radio frequency by-pass condenser, a high potential source and a resonance circuit consisting of an inductance, a capacity and a resistance.

[Oflicial Gazette May 30, 1.988.] 

